The invention pertains to filling systems for liquid storage tanks wherein tank filling is automatically terminated at a predetermined level to prevent overfill.
Tank trucks used to transport gasoline, and other liquids, usually consist of a truck-mounted tank having an opening, or pot, located at the upper portion of the tank compartment through which the compartment is filled. The driver positions the tank pot below the filling pipe or hose, and the liquid is introduced into the tank through the tank pot. In the normal practice, the operator observes the level of the liquid within the tank during filling and manually operates a shutoff valve to terminate the filling, if filling is not under the control of a preset stop-meter.
In the filling of tank trucks used to transport volatile liquids, such as gasoline, the truck driver usually fills his own truck at a storage depot. Modern gasoline storage installations for filling tank trucks used to distribute gasoline to retail outlets now usually utilize stop-meters which are preset to terminate fluid flow after a predetermined amount of gasoline has been metered. However, it occasionally happens that the operator will set the stop-meter to deliver a greater amount of liquid into the tank than the tank is able to receive. Such occurrence arises if the operator is not aware of the actual capacity of the tank compartment being filled, or more often, results from the fact that the tank compartment is partially full prior to refilling, and the operator is not aware that the tank already contains a liquid.
Such occurrences produce tank overfill through the tank pot resulting in the wasting of an expensive liquid, contamination of the environment due to the spilled gasoline, and the creation of a serious fire hazard.
When filling tanks with highly volatile liquids such as gasoline several unique problems occur. For instance, excessive splashing usually occurs during the initial stages of the filling of an empty tank which accelerates vaporization of the gasoline producing considerable fumes which quickly fill the tank and pass therefrom through the tank pot contaminating the atmosphere and also creating a potentially explosive mixture. Additionally, while it is desirable to fill the tank as quickly as possible in the interest of time, high flow rates through the hose, valves and fill conduit generate static electricity creating the possibility of producing a spark within the tank or adjacent the filling apparatus, which could ignite the gasoline fumes.
In order to minimize vaporization and agitation, deflector bases are often located at the lower end of gasoline tanker fill pipes which deflect the fuel at the bottom of the tank in such a direction as to minimize splashing and agitation. To minimize the creation of static electricity due to high flow rates, valve systems are used which permit the gasoline to flow into the tank at a reduced rate during the initial stages of filling, and once the tank is partially filled, and adequate grounding exists between the fill conduit and the tank, a greater fill rate is permitted. Such regulation of flow rates is manually regulated in prior art devices and is thereby subject to human error.